Audio, video and data information is commonly distributed recorded on magnetic tape enclosed in a plastic housing called a cassette. Many different designs of cassettes have been produced and many are still being proposed for a variety of different purposes. Currently, the most well known types are the Phillips "compact" cassette for audio and data information and the JVC "VHS" cassette for video information.
Magnetic tape is manufactured in rolls many thousands of metres long and thus sufficient for many cassettes. This tape is wound into the plastic housings of cassettes using a special machine known as a loader. The information may be recorded onto the magnetic tape after it has been loaded into the cassette ("in-cassette duplication") or before ("reel-to-reel duplication"). If it is recorded onto the tape before being wound, many copies of the information may be recorded on one roll of tape. A magnetic marker known as a cue tone is recorded between each copy of the information in order that the loader can detect the correct point to complete one cassette and start the next.
In analog audio cassette production (and some data cassettes), programme material can be recorded in reel-to-reel duplication onto use tape, special machines having been developed for this purpose. Typically, use tape equivalent to about 30 to 40 C60 cassettes is recorded in this way.
This arrangement inevitably means that audio cassette reel-to-reel recording equipment is somewhat bulky, a recording deck having a relatively large surface area in order to accomodate the supply spool and take-up spool in side-by-side relationship. In practice, however, this is a relatively minor disadvantage in a conventional audio context. The recorded signals have a comparatively small band width in conventional audio copying such that recording can be carried out at a very high speed without loss of recording quality. For example, recording may be carried out at from 32 to 128 times playback speed. This enables highly productive audio cassette recording operations to be set up with relatively few copier machines so that the relative bulk of the machines is at least tolerable.
In video recording, the recorded signals are of much higher bandwidth. Recording of such signals cannot be carried out at high speed without serious loss of recording quality. Even a recording speed 50% higher than playback speed will normally result in an unacceptable drop in quality so that in general recording speed will be equal to retrieval or playback speed.
Because of this relatively slow speed of recording, many more copiers are needed for video copying than in audio recording, several thousands of copiers typically being used in video copying. Video copiers having the bulk of audio open spool copiers would require about 400 percent more space than an in-cassette copier and this is totally unacceptabe. The same applies to high bandwidth audio copying e.g. R-DAT and S-DAT format.
For these reasons, slow speed in-cassette copying of video tapes has remained customary practice since the relevant cassette formats were introduced. However, the method has always been regarded as unsatisfactory for a number of reasons. First, the process is labour intensive due to the requirement to change the cassette after each transfer of information. Secondly, the mechanisms which handle the cassettes in the players are inherently complex and sufficiently prone to unreliable performance that they can give significant practical problems in a heavy usage environment. Thirdly, since the players have to start and stop in-between each cassette and each cassette contains tape which may have come from different rolls of varying quality, it is neccessary to sample each one after the recording is complete to ensure the process has proceeded correctly.
Finding a solution to the problems and particularly the slow production speed of existing video copiers has been the subject of much activity in the industry. This has largely been without success. One proposal which has achieved a measure of success, however, is the Sony Sprinter system. In this system, a master tape is passed in contact with a slave tape through a recording station at which the two tapes are pressed together so that recording onto the slave tape takes place by induced print-through. Although this system can operate at high speed (since the two tapes are stationary relative to one another at the print station), quality recording requires a very strongly recorded master tape which is difficult to produce, production requiring specialist expensive recording techniques. The print-through recorder is also itself expensive to produce since video copiers for commercial cassette production operations represent a small market, whose supply involves the economic disadvantages of small scale production operations. Such economic disadvantages are, of course, avoided in the case of conventional direct cassette copiers since these are closely modelled on similar video cassette copying equipment mass produced for the very large international domestic market (or are indeed identical machines).
Tape transport involving concentric spools, i.e. a take-up and supply spool rotatable on a common shaft so as to have parallel juxtaposed planes of rotation, has been employed in certain applications. However, this system has not previously been proposed for recording of large bandwidth material such as is the case in video recording.